In 3,876 autopsies performed between 1964 and 1974 in adult Hong Kong Chinese, the incidence of pulmonary thromboembolism was 0.75%. In a prospective study of 70 autopsies, the right lungs were inflated, fixed, slab-sectioned, and studied for pulmonary thromboembolism. Twenty-seven per cent had evidence of pulmonary thromboembolism, although in only one case was the lesion the cause of death. In another 62 autopsies, routine dissection of pelvic and both lower extremity veins revealed that 18% had evidence of thrombosis. Eighty-three per cent of these had pulmonary thromboembolism; in 3 of these 62 cases (5%) pulmonary thromboembolism was the cause of death. Massive pulmonary thromboembolism in the Hong Kong Chinese is much less frequent than in Caucasians. The finding of many small asymptomatic pulmonary thromboemboli in both racial groups suggests that pulmonary circulation performs a physiologic filtering function. The rarity of massive clots in the Chinese warrants further investigation and special attention to biomechanics of thrombosis formation and detachment.